The developer behind Quincy’s $1.6 billion downtown redevelopment said farewell on Thursday, signaling the death of the project in its current form.

In an advertisement in Thursday’s Patriot Ledger newspaper, Street-Works Development LLC said it could not move forward with the envisioned downtown redevelopment and would probably default on the project’s overriding contract, known as the Land Disposition Agreement.

“Drawing on thirty years of experience as developers and consultants, we firmly believe that financing and building new construction development in the downtown is impossible today,” said the ad, which was written as a letter to Mayor Thomas P. Koch. “Specifically, the existing Land Disposition Agreement contains prohibitive conditions relating to project cost . . . we at Street-Works cannot presently foresee how these obstacles will resolve.”

The company thanked the mayor for allowing Street-Works to share “your hopes and dreams for a great downtown” and said it hopes to play a role in the redevelopment.

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The letter comes after city officials told Street-Works it had 30 days to begin the next phase of the redevelopment or it would be in default of the city agreement. That deadline expires next Friday.

Koch said Thursday that city officials are discussing how to proceed. Though the contract states that the city’s “sole remedy” to a default is to terminate the agreement, Koch said Street-Works won’t be automatically kicked out of the redevelopment.

“I’d have to put them on notice and officially cut ties,” Koch said, adding that there is no timeline for that decision.

However, Koch did say that one option going forward is to split the city into redevelopment sections and use several developers.

“We’ll be entertaining a new approach,” Koch said. “We may not do this with one master developer. Those are the things we’re looking at now. We may break it up into parts.”

What is certain, Koch said, is that actions after the deadline will be swift.

“Time is precious, and we’re in a development cycle I don’t want to miss,” Koch said.

The shift is the latest in the kaleidoscopic transformation of the downtown project. Early plans called for the transformation of a 10-block area into stores, restaurants, and 1,100 new residences.

Yet it has been in limbo since work stopped on the first block of construction in November.

Street-Works officials did not return requests for comment Thursday. But they previously said that work halted because of escalating construction costs and proposed a more modest redesign featuring shorter buildings that would take up more land.

Yet the project remained stalled and investors said in February they will take over construction of the first step with a different developer.

Koch said that one idea would be to split the redevelopment project down Hancock Street, with the Hancock parking lot and Ross Parking Garage developed separately. Further divisions would complicate property boundaries, but Koch said his team is studying such options.

“Even if we break it into pieces, it’s the goal to keep the master plan and the mix we want very similar,” Koch said. “We can’t have five people doing the same thing. There has to be some coordination even if it’s broken up between the parties.”

City Councilor Doug Gutro, who chairs the Downtown Committee, said the city had a meeting scheduled for March 31 to talk about the legal issues involved in the next steps.

“Myself and my colleagues are interested to know what the final fate of the agreement is with Street-Works and what the administration has in terms of plans moving forward,” Gutro said.

Whatever the plan, Koch said, the city held the reins and the work done to date had set the stage for progress.

Furthermore, he said, the city is hearing from interested parties who could become involved.

“We’re still in a good place … we’ll put this back together rather quickly,” Koch said.

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